1. Field of the Invention
The present invention generally relates to tape drives and, more particularly, recording (or read/write) heads of tape drives adapted to reduce or control track mis-registration (TMR) to facilitate recording with increased track density, which leads to increased storage capacity.
2. Relevant Background
Tape drives have been widely employed in industry for over thirty years due to their ability to store large amounts of data on a relatively small and inexpensive removable format. Typically, tape drives use a storage tape that is wound between a pair of tape reels as data is transferred to or from the tape media via a read/write tape head assembly. In one arrangement, one of the reels (e.g., the “take-up” reel) is part of the tape drive while the other reel (e.g., the “cartridge” or “supply” reel) is part of a removable cartridge. Upon insertion of the cartridge into the tape drive, the storage tape on the cartridge reel is coupled to the take-up reel of the tape drive (e.g., via respective leaders). After coupling, the tape is unwound from the cartridge reel, moved past the tape head assembly and wound onto the take-up reel via a drive motor. Next, the tape is unwound from the take-up reel, moved past the tape head assembly and wound onto the cartridge. Subsequently, the storage tape is uncoupled from the take-up reel, prior to removing the cartridge from the tape drive. In another arrangement, both reels are part of a cassette which is inserted into a tape drive and driven by a drive motor.
To increase the storage density and reduce the access time of magnetic tapes, a popular trend is towards multi-head, multi-channel head structures with narrowed recording gaps and data track widths so that many linear data tracks may be manipulated on a tape medium of a predetermined width (e.g., such as one-half inch width tape) passing by the head structures at increasingly faster rates of speed. However, various factors work against the ability of existing and planned tape drives to achieve such increased storage densities and reduced access times.
In a tape drive system, the misalignment of a data reader to a previously written track is a critical factor that affects capacity. In the data storage industry, this misalignment is typically referred to as track mis-registration (TMR), and TMR is affected by many variables with one of the largest variables being tape dimensional stability (TDS). TMR due to TDS is generally calculated by multiplying a tape distortion factor of a particular media (e.g., magnetic storage tape used in a tape cartridge used with a tape drive) by one half the writer element span of a recording head of read/write head assembly. The writer element span is a linear measurement of the distance between outer elements on a bump of the recording head. TMR due to TDS is caused by changes in the width of the media or tape between the time it is written by write elements and the time it is later read by read elements, and these changes in width can be due to factors (that together define the tape distortion factor) such as the media's coefficient of thermal expansion, creep, and coefficient in tension.
TMR can limit how many tracks can be written on tape, and, as a result, TMR needs to be addressed during the design of recording heads because the industry's goal for each new generation of tape drives is to double the capacity for a particular tape width. For example, a typical product evolution for a tape drive would be to design a head to have the same number of write elements (e.g., 32 elements) but space these elements closer together so as to span half the width of those in a previous generation head (i.e., to have a write element span that is reduced by fifty percent). The number of servo bands then would be doubled on the media, which would require the development of a new servo pattern. Further, the new tape drive may have to meet the design requirement that it be able to read tapes written by the previous generation tape drives and to write tapes that are readable by the previous generation tape drives. To meet these additional requirements, the new tape drive would include additional read and write elements at the channel spacing (e.g., distance between elements on a bump of a head) of the previous generation.
Using this type of head design for each new generation can cause a number of problems or create design and manufacturing challenges. The addition of numerous elements to a head at a tighter pattern and to provide legacy read/write abilities and creation of a new servo pattern adds significantly to the cost and complexity of the tape and the recording head. Further, spacing a particular number of write and/or read elements (e.g., 32 elements) in half a previous span is also a concern due to added manufacturing complexities and due to increased problems with cross talk between the head elements.
As a result, there remains a need for a new design for a tape drive head assembly (or recording head assembly) that is configured to reduce TMR due to TDS so as to allow recording at increased track densities so as to increase capacity.